The invention relates to machine tools and more particularly to planetary-type lapping machines and to methods for lapping of a group of workpieces on such machines.
The machines of the above-mentioned type are designed for machining parallel surfaces of components of hard and fragile materials with a free abrasive tool, such as for machining of piezoquartz plates having a thickness of up to 100 mcm, and such machines are provided with a mechanism for kinematic dressing of lapping tools during machining.
Known planetary-type lapping machines comprise a lower lapping disc and an upper lapping disc and cages containing components being machined which are arranged between the discs and driven by a sun gear and a ring gear of a sun-and-planet gear which are rotated on vertical shafts coaxial with the stationary lower lapping disc and rotary upper lapping discs (lapping tools). In such machines, circumferential speeds of the cage center relative to the surface of the lapping discs are about equal and opposite, and there is provided a mechanism for rotating the upper lapping disc which is driven by one of the links of the sun-and-planet gear of the machine (cf. USSR Inventor's Certificate No. 1492911).
Alongside with the advantages of such construction of the machine consisting in that there is provided a stationary base surface (lower lapping disc), the cage is relieved because forces of friction of the plate over the surface of the lapping discs are directed at an obtuse angle, and there is a possibility of movement of the workpieces being machined along spiral paths, there are also a number of disadvantages, such as discussed hereinbelow.
The plates being machined can only move, over the surfaces of the lapping tools, along "circular" paths which results in an increased wear of teeth due to a large number of plates being machined in the cage and high circumferential speed of the cage teeth relative to the teeth of the sun and ring gears of the sun-and-planet gear. The cage size is equal to the size of the sun gear so that it is impossible to make a machine having narrow lapping tools and smaller cages which is especially important in machining thin plates.
It is known that the smaller the cage, the lower the number of plates loaded therein, hence the lower the resultant force (composed of all friction forces acting on each plate) applied to the cage. With the cage and sun gear sizes being equal, reduction of the cage dimensions results in reduced dimensions of the lapping discs and lower number of concurrently machined plates, hence productivity decreases.
Where the equality of sizes of the cage and sun gear is not required, a machine with smaller cages and a larger number of them may be made. Therefore, with the same outside dimensions of the lapping discs, the number of concurrently machined plates remains the same since a larger number of smaller cages are loaded in the machine.
Known machines, such as the lapping machine AL-2 manufactured by Peter Wolters (West Germany) provide for kinematic dressing by concurrently reversing the lower and upper lapping discs; it is, however, impossible to machine thin plates to high accuracy using such machine, since both lapping discs are rotatable. The reverse of the upper lapping disc with the stationary lower lapping disc would not bring about a desired result because the cages could not be unloaded, hence minimum thickness would be unobtainable.